Both VAWT and HAWT History

WIND TURBINES

Introduction

Types of Wind Turbines

Although there are many different wind turbine designs, they are broadly grouped in two categories based on the orientation of the axis of rotation: Horizontal Axis Wind turbines , Or HAWT, the most common type of wind turbine , and Vertical Axis Wind Turbines , or VAWT.

HAWT

Modern HAWTs usually feature rotors that resemble aircraft propellers, which operate on similar aerodynamic principles , i.e , the air flow over the airfoil shaped blades creates a lifting force that turns the rotor , the nacelle of a HAWT houses a gearbox and generator , HAWT can be placed on tower to take advantage of higher winds farther from the ground . The capture area of a HAWT, the area over which the sweeping blades can “Capture “ the wind. However, this capture area must face directly into the wind, to maximize power generation . So HAWTS require a means for alignment (yawing mechanism) so that then entire nacelle can rotate into the wind .

The are two main types of VAWT, the Savnius and the Darrieus. The Savonius operates like a water wheel using drag forces , while the Darrieus uses blades similar to those used on HAWS. VAWTs typically operate closer to the ground , which has the advantage of allowing placement of heavy equipment, like the generator and gearbox, near ground level rather than in the nacelle, However , winds are lower near ground level , so far the same wind and capture area , less power will be produced .

Another advantage of TYPMAR 300w & 600w 1000W MVAWT over the HAWT is that it doesn’t require a yaw mechanism , since it can harness wind from any direction .

For 3kw-96v maglev wind turbine , there are hydraulic braking system and patent yaw system if wind speed is very strong like TYPHOON .

If This advantage is outweighed by many other disadvantages , including : time varying power output due to variation of power during a sigle rotation of the blade, the nee for guy wire to support the tower and A new fact that TYPAMR Darrieus VAWT can be self starting like HAWTS .

Lift and Drag Airflow over any surface creates two types aerodynamic forces –drag forces , in the direction of the airflow , and lift forces , perpendicular to the airflow , Either or both of these can be used to generate the forces needed to rotate the blades of a wind turbine.

Drag-based wind turbine

In drag-based wind turbines the force of the wind pushes against a surface, like an open sail .

In fact , the earliest wind turbines , dating back to ancient Persia , used this approach . The Savonius rotor is a simple drag-based windmill that u can make a home. It works because the drag of the open, or concave, face of the cylinder is greater than the drag on the closed or convex section .

Lift-based wind turbine Concept :

More energy can be extracted from wind using lift rather than drag, but this requires specially shaped airfoil surfaces, like those used on airplane winds. The airfoil shape is designed to create a differential pressure between the upper and lower surfaces, leading to a net force in the direction perpendicular to the wind direction. Rotors of this type must be carefully oriented (the orientation is referred to as the rotor pitch.) to maintain their ability to harness the power of the wind as wind speed changes.

Magnetic levitation is an extremely efficient system for wind energy.

The full-permanent magnet system employs neodymium (“rare earth”) magnets and there is no energy loss through friction. This also helps reduce maintenance costs and increases the lifespan of the generator.

Here is how it works: the vertically oriented blades of the wind turbine are suspended in the air above the base of the machine, replacing the need for ball bearings.

Differences Between Star and Delta Connections

Differences Between Star & Delta Connections

By Dragos Lucian Cade, eHow Contributor

The Star Connection

The star or "Y" connection brings three voltage sources to a common point. In some instances, a neutral fourth wire is connected at the same point to alleviate problems if one of the voltage sources fails to open.

The Delta Connection

The delta connection is thus named because of its resemblance to the Greek sign "delta," which looks like a triangle. In such a configuration each side of the triangle contains a voltage source and there is no common point of connection. Because of this configuration, there is no need for a neutral wire, as one of the sources could fail to open without affecting the voltage or current in the system.

Advantages of Y Over Delta

While the star connection is certainly susceptible to failing to open, the configuration also allows for a smaller current to run through the wire. Therefore, a smaller gauge wire is required. This may not seem like a big consideration, but when thousands of feet of wire are being used, even a slight difference in the thickness of wire used can translate into hundreds of pounds of copper.

Advantages of Delta Over Y

As noted, the delta connection's primary advantage is the ability not to affect the system significantly even if one of the sources fails to open or is turned off. For this reason, delta configurations are considered more reliable even though greater line currents are generated

**Typhoon Kills HAWT at Hainan Island in China **

Typhoon Rammasun's violent winds and heavy rains are continuing a destructive path, killing more than hundreds HAWT in Hainan Island in China. The typhoon regained strength over the South China Sea and made landfall in China with winds exceeding 200 kilometers an hour, making it the strongest storm to hit the area in 41 years. Heavy rains are expected to lash northern China early this week. A new storm, Matmo, could bring another round of heavy wind and rains to the same areas battered by Rammasun.

Three-phase Y and Delta configurations

Initially we explored the idea of three-phase power systems by connecting three voltage sources together in what is commonly known as the “Y” (or “star”) configuration. This configuration of voltage sources is characterized by a common connection point joining one side of each source. (Figure below)

Three-phase “Y” connection has three voltage sources connected to a common point.

If we draw a circuit showing each voltage source to be a coil of wire (alternator or transformer winding) and do some slight rearranging, the “Y” configuration becomes more obvious in Figure below.

Three-phase, four-wire “Y” connection uses a "common" fourth wire.

The three conductors leading away from the voltage sources (windings) toward a load are typically called lines, while the windings themselves are typically called phases. In a Y-connected system, there may or may not (Figure below) be a neutral wire attached at the junction point in the middle, although it certainly helps alleviate potential problems should one element of a three-phase load fail open, as discussed earlier.

Three-phase, three-wire “Y” connection does not use the neutral wire.

When we measure voltage and current in three-phase systems, we need to be specific as to where we're measuring. Line voltage refers to the amount of voltage measured between any two line conductors in a balanced three-phase system. With the above circuit, the line voltage is roughly 208 volts. Phase voltage refers to the voltage measured across any one component (source winding or load impedance) in a balanced three-phase source or load. For the circuit shown above, the phase voltage is 120 volts. The terms line current and phase current follow the same logic: the former referring to current through any one line conductor, and the latter to current through any one component.

Y-connected sources and loads always have line voltages greater than phase voltages, and line currents equal to phase currents. If the Y-connected source or load is balanced, the line voltage will be equal to the phase voltage times the square root of 3:

However, the “Y” configuration is not the only valid one for connecting three-phase voltage source or load elements together. Another configuration is known as the “Delta,” for its geometric resemblance to the Greek letter of the same name (Δ). Take close notice of the polarity for each winding in Figure below.

Three-phase, three-wire Δ connection has no common.

At first glance it seems as though three voltage sources like this would create a short-circuit, electrons flowing around the triangle with nothing but the internal impedance of the windings to hold them back. Due to the phase angles of these three voltage sources, however, this is not the case.

One quick check of this is to use Kirchhoff's Voltage Law to see if the three voltages around the loop add up to zero. If they do, then there will be no voltage available to push current around and around that loop, and consequently there will be no circulating current. Starting with the top winding and progressing counter-clockwise, our KVL expression looks something like this:

Indeed, if we add these three vector quantities together, they do add up to zero. Another way to verify the fact that these three voltage sources can be connected together in a loop without resulting in circulating currents is to open up the loop at one junction point and calculate voltage across the break: (Figure below)

Sure enough, there will be zero voltage across the break, telling us that no current will circulate within the triangular loop of windings when that connection is made complete.

Having established that a Δ-connected three-phase voltage source will not burn itself to a crisp due to circulating currents, we turn to its practical use as a source of power in three-phase circuits. Because each pair of line conductors is connected directly across a single winding in a Δ circuit, the line voltage will be equal to the phase voltage. Conversely, because each line conductor attaches at a node between two windings, the line current will be the vector sum of the two joining phase currents. Not surprisingly, the resulting equations for a Δ configuration are as follows:

With each load resistance receiving 120 volts from its respective phase winding at the source, the current in each phase of this circuit will be 83.33 amps:

So each line current in this three-phase power system is equal to 144.34 amps, which is substantially more than the line currents in the Y-connected system we looked at earlier. One might wonder if we've lost all the advantages of three-phase power here, given the fact that we have such greater conductor currents, necessitating thicker, more costly wire. The answer is no. Although this circuit would require three number 1 gage copper conductors (at 1000 feet of distance between source and load this equates to a little over 750 pounds of copper for the whole system), it is still less than the 1000+ pounds of copper required for a single-phase system delivering the same power (30 kW) at the same voltage (120 volts conductor-to-conductor).

One distinct advantage of a Δ-connected system is its lack of a neutral wire. With a Y-connected system, a neutral wire was needed in case one of the phase loads were to fail open (or be turned off), in order to keep the phase voltages at the load from changing. This is not necessary (or even possible!) in a Δ-connected circuit. With each load phase element directly connected across a respective source phase winding, the phase voltage will be constant regardless of open failures in the load elements.

Perhaps the greatest advantage of the Δ-connected source is its fault tolerance. It is possible for one of the windings in a Δ-connected three-phase source to fail open (Figure below) without affecting load voltage or current!

Even with a source winding failure, the line voltage is still 120 V, and load phase voltage is still 120 V. The only difference is extra current in the remaining functional source windings.

The only consequence of a source winding failing open for a Δ-connected source is increased phase current in the remaining windings. Compare this fault tolerance with a Y-connected system suffering an open source winding in Figure below.

Open “Y” source winding halves the voltage on two loads of a Δ connected load.

With a Δ-connected load, two of the resistances suffer reduced voltage while one remains at the original line voltage, 208. A Y-connected load suffers an even worse fate (Figure below) with the same winding failure in a Y-connected source

Open source winding of a "Y-Y" system halves the voltage on two loads, and looses one load entirely.

In this case, two load resistances suffer reduced voltage while the third loses supply voltage completely! For this reason, Δ-connected sources are preferred for reliability. However, if dual voltages are needed (e.g. 120/208) or preferred for lower line currents, Y-connected systems are the configuration of choice.

REVIEW:

The conductors connected to the three points of a three-phase source or load are called lines.

The three components comprising a three-phase source or load are called phases.

Line voltage is the voltage measured between any two lines in a three-phase circuit.

Phase voltage is the voltage measured across a single component in a three-phase source or load.

Line current is the current through any one line between a three-phase source and load.

Phase current is the current through any one component comprising a three-phase source or load.

In balanced “Y” circuits, line voltage is equal to phase voltage times the square root of 3, while line current is equal to phase current.

In balanced Δ circuits, line voltage is equal to phase voltage, while line current is equal to phase current times the square root of 3.

Δ-connected three-phase voltage sources give greater reliability in the event of winding failure than Y-connected sources. However, Y-connected sources can deliver the same amount of power with less line current than Δ-connected sources